1. Field of the Invention
The present invention relates generally to spiral tubes and pipes formed by spiralled, joined strips.
2. Definitions and Applicability
The present invention is applicable to spiral tubular products generally, including both tubes and pipes. Frequently here for brevity, we use one word or the other, but it is understood the invention is applicable to both. Also, although the exemplary system forms smooth wall tubular products, it will be readily apparent to those familiar with the technology that the. invention is applicable, in addition to smooth wall tubular products, to profiled (including sinusoidal or corrugated) tubular products.
3. Current State of the Relevant Field
Typically, spiral tubes and pipes are formed to a constant diameter. The relevant factors, (1) strip width, (2) angle of strip entry into the rolls, and (3) the position of the pressure roll relative to the other rolls, are held constant to maintain the desired diameter. Several approaches are available in the technology to prevent diameter deviations and thus maintain diameter control in such a system. For example, commonly assigned U.S. Pat. Nos. 3,650,015 and 3,940,962 describe equipment and methods for forming spiral tubular products. The ""015 patent describes a unique free-forming approach for forming parallel wall corrugated tubes. The ""962 patent discloses methods and apparatus for controlling the diameter of spiral tubing made with a three-roll mill by displacing the joined edges of the helical convolutions radially relative to the longitudinal axis of the tubing to correct for diameter deviations. The ""015 and ""962 patent are incorporated by reference.
In one aspect, the present invention is embodied in apparatus for forming tapered spiral tubes from strips, which comprises a tube forming system which forms a strip of material such as metal into a spiral tube; and a strip infeed system which is adapted for feeding a strip to the spiral tube forming system. The tube forming system and the strip infeed system are adapted for pivotal movement relative to one another to vary the helix angle between these components and thus vary the diameter of the resulting spiral tube. The apparatus further includes a drive system for effecting the desired pivotal movement between the strip infeed system and the tube forming system; and a computer system which is operatively connected to the motor drive system for operating the motor drive system to vary the helix angle as required.
In another embodiment, the strip infeed system itself is adapted for pivotal movement relative to the tube forming system to vary the helix angle. In yet another embodiment, the strip infeed system is mounted on wheels for pivotal movement relative to the tube forming system to effect the desired variation of the helix angle. In a preferred embodiment, the tube forming system is a three roll system comprising cooperating lead roll, buttress roll and mandrel sets.
Other aspects and embodiments of the present invention are described in the specification, drawings and claims.